METEOROLOGY. 477 



nary mean barometric pressure from the same source is 2G'".9G2517, tlie true 

 mean 2G^". 962515 ; the first shows a difference of +0°.004, the second of 

 0.000002 inches. 



It is easy to prove that this difference (J) for a common year is represented 

 by the following equation : 



4380J = 7 {mi-\-m:i-\-m5-\-mT\-ms + nho+mi2)—29 ^2— 5 (w4+'Wg+w?9+'"ii) 

 and for a leap year: 



wliere nii m-i m^i etc, are the monthly means corresponding to the first, second, 



third, etc., month. 



Taking again the case of Caracas as an example, wo find a differeneo for tLe 



2 S'' 

 thermometric means of -^^ :=: 0°.0038 as stated above, and for the barometric 



0.0016 , , 



ineans of "yoo^ ^^ 0.0000022 as before. 



AN AfCOUNT OF A CTCIOXE, JANUARY 6 AND 7, 1867, ENCOUNTERED BY THE 

 UNITED STATES STEAMER MONOCACT, 'WHILE ON HER PASSAGE FROM 



SIMON'S BAY TO MAURITIUS, IN THE INDIAN OCEAN. 



By Nicholas Pike, United States Consul, Port Louis. 



The United States steamer Monocacy, bound from Simon's bay, South Africa, 

 towards Mauritius, met, during the passage to the last-mentioned port, one of 

 those dreaded tornadoes or hurricanes that swept over the vast expanse of the 

 South Indian ocean. Being myself on board of the Monocacy, and deeply inter- 

 ested in the science of the laws of storms, I succeeded, by careful observations 

 of barometer and thennometer, by noticing the changes of wind and tempera- 

 ture, and the rising and setting of the storm wave, to ascertain pretty correctly 

 the centre of the huixicane, and deduce all the aforesaid changes of wind and 

 weather to the rules laid down by Messrs. Piddington and Redfield, in their 

 admirable treatise on the law of storms; the oflicers of the vessel kindly supply- 

 ing me with a copy of the log, which, if even not very coiTect, greatly aided 

 me in tracing the cyclone home to its vortex. 



As my object in writing this is not a description of the storm, but especially 

 facts and dates, and arranging such in tables to prove the correctness of the 

 theory of cyclones, I shall previously insert a short description of the tempest. 

 The whole of our passage, since leaAang Simon's bay, had been a succession of 

 bad weather, and the few sunny days which we in reality had were both to 

 officers and men a veritable blessing; sails were repaired, hammocks and bed- 

 ding aired, clothes dried and mended, and the decks, for the first time quite dry, 

 resounded in every direction with the joyous laughter of the crew, carelessly for- 

 getting the past troubles, living onl}^ for the present, regardless for the future. 

 But their joy was of short duration. On the evening of the 0th of January, the 

 sky became gloomy, dark threatening clouds passed swiftly to the northward, 

 the sea rose last, and the vestcl commenced to roll heavily ; bedding and clothes 

 were quickly taken below, and everything secured for the bad weather again. 

 The night, from January 6 to 7, fully justified our anticipations ; heavy blasts of 

 wind, rain, and lightning, the rolling of the vessel, the cracking of her tind)ers, and 

 the thundering noise of a wave breaking under the vessel's counter, made, I may 

 safely say, even the oldest seamen on board uncomfortable, especially as the 

 vessel being new, and her sea- worthiness to all, even to the captain, unknown, we 

 had not that confidence in her which her o-allant behavior afterwards durinir the 



